The present invention relates to a speed increaser and a centrifugal compressor equipped with the speed increaser.
A speed increaser that transmits the rotation of a low-speed shaft to a high-speed shaft has been known in the art pertaining to the present invention. Japanese Patent Application Publication 2003-314446 discloses a speed increaser including a peripheral wall that is rotatable with the rotation of a low-speed shaft, a high-speed shaft that is disposed within the peripheral wall, and a roller that is disposed between the peripheral wall and the high-speed shaft and has an outer peripheral surface that is in contact with the inner peripheral surface of the peripheral wall and the outer peripheral surface of the high-speed shaft. The roller and the high-speed shaft are held by tightening of the peripheral wall.
According to the speed increaser of the above-cited publication, an oil film (elastohydrodynamic lubrication film) is formed at a contact area between the peripheral wall and the roller and at a contact area between the roller and the high-speed shaft with the rotation of the peripheral wall, and the rotation is transmitted through the oil film.
In order for the oil film to be formed stably during the rotation, pressure to some extent need be applied to the contact area between the inner peripheral surface of the peripheral wall and the outer peripheral surface of the roller and also to the contact area between the outer peripheral surface of the roller and the outer peripheral surface of the high-speed shaft.
Since the high-speed shaft and the roller are in contact with each other at their outer peripheral surfaces, the area surface of the contact area tends to become small. On the other hand, the peripheral wall and the roller are in contact with each other at the inner peripheral surface of the peripheral wall and the outer peripheral surface of the roller, so that the contact area between the peripheral wall and the roller is greater than that of the contact area between the high-speed shaft and the roller. Consequently, the pressure at the contact area between the peripheral wall and the roller tends to become small.
In this case, if a tightening of the peripheral wall is increased so as to increase the pressure at the contact area between the peripheral wall and the roller, there is a fear that power loss between the high-speed shaft and the roller may be increased and the high-speed shaft may be subjected to an increased load.
The present invention, which has been made in light of the above problems, is directed to providing a speed increaser that successfully transmits power from the peripheral wall to the high-speed shaft and a centrifugal compressor equipped with such speed increaser.